The present invention relates to a cathode material for a lithium secondary battery having superior sinterability and capable of exhibiting sufficient battery characteristics, and to the manufacturing method thereof.
In recent years, there is a rapidly growing demand for a non-aqueous system lithium secondary battery as a high energy density battery. This lithium secondary battery is configured from three fundamental components; namely, a cathode, an anode, and a separator retaining an electrolyte interposed between these electrodes.
As the cathode and anode, a slurry obtained by mixing and dispersing active materials, conductive materials, bonding materials and plasticizing agents (where appropriate) in a dispersion medium is used by being supported by a collector such as a metallic foil or a metallic mesh.
Among the above, as the cathode active material, a composite oxide of lithium and transition metal, in particular, cobalt composite oxide, nickel composite oxide, and manganese composite oxide are typical.
These lithium composite oxides are generally synthesized by mixing the compound of the main element (carbonate or oxide of Mn, Fe, Co, Ni and the like) and the lithium compound (lithium carbonate and the like) at a prescribed ratio, and subjecting this to heat treatment (oxidation treatment) (refer to Patent Document 1 and Patent Document 2).
Nevertheless, since these lithium composite oxides contain large amounts of impurity elements such as Na and S that inevitably get mixed in during the manufacturing process, such impurity elements would affect the sinterability and stability of composition and cause the deterioration in battery characteristics (rate characteristics).
In light of the above, the present inventors introduced chloride of one or more metal elements selected from Mn, Co and Ni in a lithium carbonate suspension in order to obtain a composite oxide containing only small amounts of Na and S (100 ppm (by mass) or less), and thereby proposed a lithium secondary battery material having a high tap density for obtaining fine powder and which stably yields superior battery characteristics (refer to Patent Document 3).
Although this lithium secondary battery material yields superior characteristics in comparison to the foregoing conventional art, there was still room for improvement regarding sinterability and battery characteristics.    [Patent Document 1] Japanese Patent Laid-Open Publication No. H1-294364    [Patent Document 2] Japanese Patent Laid-Open Publication No. H1-307094    [Patent Document 3] WO200316416 (Patent Application No. 2003-1955)